1. Technical Field
The present invention relates to metering valves, and in particular, to pintle valves, such as can be used to meter fuel in air and space vehicles.
2. Description of the Related Art
Valves for metering fuel and other combustible media to engines in aircraft and spacecraft are well known in the art, see e.g., U.S. Pat. No. 6,250,602 B1, assigned to the assignee of the present invention. Such valves are used to control the rate at which pressurized fuel, in a liquid or gaseous state, is supplied to inlet orifices in the engine combustion chambers. The valves are relied upon to provide consistent and rapid control of flow rates of fuel at ignition and during sustained operation. Their operation is critical to proper performance of the vehicle. Poor valve operation can result in unintended engine shutdown and failure.
These valves can have movable stem-like valve members, or pintles, aligned with the outlet port of the valve for controlling the rate at which fuel flows to the engine. Pintle type valves are typically less affected by the temperatures and pressures of the fuel passing through the fuel chamber of the valve, due to their contoured head and axial movement. However, even pintle valves can be adversely affected by the high pressure and temperature conditions of jet engines.
Jet engines often burn fuel in a gaseous state at elevated temperatures. The high temperature environment can cause thermal breakdown of the metering components of the valves, which can lead to improper performance or failure unless they are cooled adequately. One technique for cooling the valves is to circulate a pressurized liquid through the valves in a separate area from the gas that is relatively cool in comparison to the hot gas. The pressurized liquid not only cools the valve but also drives the metering components of the valve. To minimize weight in air and space vehicles, the liquid used to cool and drive the valves can be the pre-burned fuel in a liquid state. Such valves are known in the industry as xe2x80x9cfueldraulicxe2x80x9d valves.
Conventional fueldraulic valves typically do not provide adequate cooling for use with supersonic combustion ramjet (xe2x80x9cscramjetxe2x80x9d) engines, which fly between Mach 4 and Mach 10 in the earth""s atmosphere. Known scramjet engines can burn gaseous hydrogen-based fuel at temperatures in excess of 1000xc2x0 F. and encounter considerable external heating from the extreme environment. Typical conventional fueldraulic valves are thus unsuitable for the aggravated thermal conditions of scramjet engines.
The present invention provides an improved pintle valve particularly designed to meter high temperature media, such as gaseous jet fuel. The motive force operating the pintle which controls passage through a nozzle can be a pressurized liquid, such as liquid jet fuel. The pressurized liquid is uniquely routed through a piston chamber to cool the piston and associated components as it drives the pintle.
Specifically, the invention provides a valve actuated by a pressurized drive media to meter a primary media. A body defines a piston chamber and has a nozzle passageway axially aligned with the piston chamber about a stroke axis. The body also has drive media supply and return ports in communication with the piston chamber and primary media intake and exhaust ports in communication with the nozzle passageway. The piston chamber and supply and return ports are isolated from the nozzle passageway and intake and exhaust ports. A pintle extends along the stroke axis and has a head sized to close off the nozzle passageway. A piston is disposed in the piston chamber along the stroke axis. A baffle directs the drive media along an axial path adjacent the piston. The piston is coupled to the pintle and has a head responsive to the drive media when pressurized to drive the pintle between an open position in which the primary media intake and exhaust ports are in communication with each other and an extended position in which the pintle head closes off the nozzle passageway such that the intake and exhaust ports are not in communication with each other.
In one preferred form, the invention provides a pressurized liquid fuel driven valve for metering gaseous fuel to a jet engine of an air or space vehicle. A valve body has a main housing at least in part defining a piston chamber disposed about a stroke axis and the supply and return ports for the pressurized liquid fuel. A nozzle body extends from the main housing along the stroke axis in axial alignment with the piston chamber and having the intake and exhaust ports for passing the gaseous fuel through the throat of a venturi passageway. A seal separates the piston chamber and the supply and return ports from the venturi passageway and the intake and exhaust ports. A pintle extends along the stroke axis concentric with the venturi passageway and has a head sized to close off the throat of the venturi passageway. A piston coupled to the pintle extends from the piston chamber along the stroke axis and has a head responsive to the pressurized liquid fuel to drive the pintle along the stroke axis between the open and closed positions. A servo valve, in communication with the supply and return ports, controls flow of the pressurized liquid fuel through the piston chamber and thereby controls translation direction and speed of the piston.
The valve can thus be used to meter fuel to the combustion chambers of jet engines. The primary media is a gaseous jet fuel and the drive media is liquid jet fuel. The gaseous jet fuel is at a much higher temperature, preferably at least twice that of the liquid jet fuel. For example, the valve has been tested for successful operation for liquid jet fuel at approximately 300xc2x0 F. and gaseous jet fuel at approximately 1350xc2x0 F. The valve has also been tested for successful operation when both fuels are liquid and has the design capability of operation at low temperatures of at least xe2x88x9265xc2x0 F.
In another preferred form, the piston has a hollow core and opens at a head opposite the end to which the pintle is threaded. The piston has a radial passageway leading to this axial cavity so that drive media can pass through the piston. The baffle has a hollow core and is disposed in the piston cavity. The baffle is open at both end and has an externally threaded section contacting the piston cavity wall and thereby defining two helical flow paths. The piston rides in a piston guide fixedly disposed about the stroke axis within the piston chamber. The piston guide has an inner diameter against which a piston head slideably seals and an outer annular channel sealed against the piston chamber at one axial end and defining a passageway at a downstream axial end. A high temperature seal is disposed about the piston beyond the downstream end of the piston guide separating the drive media from the primary media.
This arrangement directs the drive media from the supply port to the annular channel around the piston guide and across the face of the seal, through the passageway in the piston, between the piston and the baffle, through the dual thread paths, back through the interior of the baffle and out the opening at the piston head. This arrangement facilitates the metering of very hot gaseous fuel as required for some jet engines, scramjet engines. The relatively cool liquid fuel circulates round the piston guide, through the outer and inner diameter of piston body and around the face of the primary seal isolating the liquid fuel from the gaseous fuel. The piston guide is purposely placed upstream from the main seal to reduce thermal distortion (and thus binding) between the guide and piston that could otherwise occur as a result of the large temperature gradient between the gas and liquid areas of the valve. The dual threads create ideal flow paths for proper heat transfer from the piston.
In another preferred embodiment, an electronic control unit provides an input signal to a servo valve for controlling flow of the drive media through the valve and the supply and return ports. A position transducer, preferably a linear variable differential transformer, is disposed along the stroke axis in the center of the baffle. The position transducer has a sensing coil (not shown) fixed with respect to the body and a metallic probe coupled to the piston and movable within the center of the coil. The position transducer provides a feedback signal to the control unit corresponding to the position of the piston (and thus the position of the pintle with respect to the nozzle passageway). The control unit can adjust the input signal supplied to the servo valve in response to the feedback signal.
The present invention thus provides a highly accurate metering valve in which deviations in the actual position of the pintle (and thereby flow rate of the gaseous fuel through the nozzle) are corrected electronically to match the input signal to the valve. This closed-loop position-feedback control also improves the dynamic response of the valve.
In yet another preferred form, the nozzle passageway is a venturi passageway having a narrowed throat that can be sealed by the pintle head. The venturi passageway provides sonic velocity flow through the throat to reduce noise without high pressure losses in the nozzle.
In still another preferred form, the valve body is defined by a main housing and a removable nozzle body secured to the main housing by a threaded collar. The venturi passageway is defined by a removable nozzle module. The nozzle module can be interchanged with others of different configurations or throat sizes and the pintle can be interchanged with others of different size or configuration, access thereto be gained by removing the nozzle body. Thus, the valve is highly customizable for varying the flow and metering characteristics of the valve.
The valve body can also be a suitable manifold for a multi-valve array designed to meter fuel to the injectors of each combustion zone in a jet engine. In one preferred form, the body defines five sets of piston chambers with the drive liquid passing in parallel through each chamber after entering the supply port of one chamber and being routed to the next chamber through a parallel outlet port of the first chamber and subsequent chambers.
These and still other advantages of the invention will be apparent from the detailed description and drawings. What follows is a preferred embodiment of the present invention. To assess the full scope of the invention the claims should be looked to as the preferred embodiment is not intended as the only embodiment within the scope of the invention.